A conventional strain detector of this type has a configuration as shown in FIG. 19 and FIG. 20.
FIG. 19 is a bottom view of a conventional strain detector, and FIG. 20 is a perspective view of the strain detector. In FIG. 19 and FIG. 20, insulating substrate 1 is formed from elastic material, which is disposed at the bottom of pressing member 2. Also, four strain resistance elements 3 are provided at the bottom of the insulating substrate 1. The strain resistance elements 3 are electrically connected to a pair of power electrodes 4, a pair of output electrodes 5, and a pair of GND electrodes 6, thereby forming a bridge circuit.
The operation of a conventional strain detector having such a configuration will be described in the following discussion.
As shown in FIG. 21, when a pressing force is applied by pressing member 2 to the top nearly at the center of insulating substrate 1 after fixing a conventional strain detector on fixing member 7 by using male screws 8, a bending moment is generated in insulating substrate 1 due to the pressing force. Due to the bending moment, a bending moment is also generated in each of four strain resistance elements 3 disposed at the bottom of insulating substrate 1. And, when a bending moment is generated in strain resistance element 3, it causes the resistance value of strain resistance element 3 to change. Accordingly, the change of the resistance value is outputted from a pair of output electrodes 5 to an external computer (not shown), and thereby, the pressing force applied to insulating substrate 1 is measured.
Such a conventional strain detector is, for example, disclosed in Japanese Laid-Open Patent H8-87375.